Police say the men took turns raping the woman, using an iron rod to violate her as the bus drove around the city for almost an hour. When they had finished, they dumped the two victims by the side of the road.
The woman's injuries were so severe that some internal organs had to be removed. She died two weeks later at a hospital in Singapore.
"This is an extreme case of depravity" Krishnan, the prosecutor, said.
A rape every 22 minutes
As in many countries, rape is a grimly frequent occurrence in India.
According to Indian government statistics, a woman is raped every 22 minutes on average.
But the New Delhi attack seized the country's attention.
Advocates criticized the world's largest democracy for failing to protect half of its population. Protesters demanded better treatment of women and decried the apathy of police and the judicial system.
The government passed tougher anti-rape laws, introducing the death penalty for repeat offenders, and imprisonment for acid attacks, human trafficking and stalking.
But some Indians say that while the laws on crimes against women have changed, mindsets and enforcement have been slower to adjust.
'Take it to the source'
Government figures show that the number of women reporting rapes has risen significantly since the New Delhi attack and the heavy scrutiny that followed it.
Observers say it indicates that women who are victims of sexual attacks feel more emboldened to come forward than they did before.
Prosecution of such crimes has improved, Bedi believes, but it will take a heavy emphasis on the family and school environments to resolve the problem in the long run.
"You can't just begin and end with the police and the prosecution and the courts," she said. "You have to go backward and take it to the source."